Quartz porphyry in Yuejinshan Fe-polymetallic deposit is one of the rock masses, which formed the granite belt relating to the late Yanshanian skarn-type Fe-polymetallic deposits in the eastern Heilongjiang, and is al...Quartz porphyry in Yuejinshan Fe-polymetallic deposit is one of the rock masses, which formed the granite belt relating to the late Yanshanian skarn-type Fe-polymetallic deposits in the eastern Heilongjiang, and is also closely related to the metallogenic space of the Fe-polymetallic deposits. Quartz porphyry has the zircon U-Pb concordia age of 125.0±1.1 Ma, overall showing high Si(SiO_2=74.48%--75.00%), rich alkaline(Na_2O+K_2O=7.93%--8.17%, K_2O/Na_2O=1.39--1.46), and poor Mg(MgO=0.27%--0.31%), with the A/CNK value being 0.95--0.99, having the characteristics of obvious enrichment of LREE and medium Eu negative anomaly(0.69--0.74), indicating that the rock belongs to quasi-aluminous high potassium calc-alkaline series and has the same characteristics as those of the I-type granite. The rock is also characterized by the enrichment of LILE and active incompatible elements, and depletion of HFSE such as Nb, Ta, P and Ti, with the Mg~# value being 32--37, indicating that the rock originated from partial melting of crustal materials. It can be concluded from the above characteristics or data and from the distribution of contemporary magmatic rocks in the area, that quartz porphyry in Yuejinshan Fe-polymetallic deposit was formed in a tectonic background of the subduction of the paleo-Pacific plate in late Yanshanian.展开更多
The Shilu Fe-polymetallic ore deposit,a famous hematite-rich Fe-ore deposit,is situated at the western Hainan Province of south China.The deposit characterizes the upper Fe ores and the lower Co-Cu ores,which are main...The Shilu Fe-polymetallic ore deposit,a famous hematite-rich Fe-ore deposit,is situated at the western Hainan Province of south China.The deposit characterizes the upper Fe ores and the lower Co-Cu ores,which are mainly hosted within a low-grade to medium-grade,dominantly submarine metamorphosed siliciclastic and carbonate sedimentary succession of the Neoproterozoic Shilu Group.Three facies types of metamorphosed BIFs,i.e.the oxide facies,the silicate-oxide facies and the sulfide-carbonate facies BIFs,are identified within the sixth sequence of the Shilu Group.The oxide facies BIF(i.e.the Fe-rich itabirites or ores)consists of alternating hematite-rich microbands with quartz-rich microbands;the silicate-oxide facies BIF(i.e.the Fe-poor itabirites or ores)comprises alternating millimeter-to a few tens meter-scale,magnetite-hematite-rich bands with calcsilicate-rich(garnet+actinolite+diopside+epidote+quartz)meso-to microbands;and the sulfide-carbonate facies BIF(i.e.the Co-Cu ores)contains alternating macro-to mesobands of Co-bearing pyrite and pyrrhotite,and chalcopyrite with mesobands of dolomite+calcite+diopside+quartz and/or chlorite+sericite+quartz.The blastooolitic,blastopelletoid blastocolloidal and blastopsammitic textures,and blasobedding structures which most likely represent primary sedimentation are often observed in these BIF facies.The interbedded host rocks with the BIFs mainly are the pyroxene-amphibole rocks and the banded or impure dolostones,and also contain banded or laminated structures,and lepido-gra-noblastic,nematoblastic and/or blastoclastic textures.Compositionally,the main host rocks,the pyroxene-amphibole rocks contain basic-intermediate SiO_2(~54.00 wt.%),CaO(~14.19 wt.%),MgO(~9.68 wt.%)and Al_2O_3(~8.49 wt.%)with a positive correlation between Al_2O_3 and TiO_2.The UCC-like Zr and Hf abundances,high Ba content andεNd(t)value(^-5.99)as well as the ratios of La/YbPAAS(0.17~1.00),δEuPAAS(0.88~1.12)andδCePAAS(0.93~1.13)commonly reveal that the protoliths to this type rocks are hydrogenic with a large contribution of terrigenous sediments and minor hydrothermal input.The high CaO+MgO+LOI contents and the extremely low trace element and REEconcentrations as well as the ratios of Y/Ho(44~45),δEuPAAS(1.13~1.57)andδCePAAS(0.69~0.98)reflect a marine origin with minor terrigenous materials for the banded or impure dolostones.Moreover,this type rocks also account for a negativeεNd(t)value(^-7.49).The oxide facies BIF is dominated by Fe_2O_3+FeO(~75.59wt.%)and SiO_2(~20.47 wt.%)with aεNd(t)value of^-6.10.The variable contents in Al_2O_3,TiO 2,K2O,Na2O,Zr,Hf and∑REE,and variable ratios of Y/Ho(24~39)andδEuPAAS(0.86~11.07)suggest the precursor sediments to this facies BIF are admixtures of sea-floor hydrothermal fluids and seawaters with minor involvement of detrital components.Compared to the oxide facies BIF,the silicate-oxide facies BIF is lower in Fe_2O_3+Fe O(~39.81wt.%)and Ba but higher in SiO_2(~42.54 wt.%),Al2O3(~3.60 wt.%),TiO_2(~0.19 wt.%),MgO(~1.12 wt.%),CaO(~9.06 wt.%),K_2O(~0.98 wt.%),Mn and Zr.The ratios of Y/Ho(25~34),La/YbPAAS(0.14-0.74)andδEuPAAS(0.91~1.12)most likely are linked to higher degree of detrital contamintants.While the sulfide-caronate facies BIF is main but variable in Fe_2O_3+Fe O(15.79~57.91 wt.%),SiO 2(0.54~61.52 wt.%),MgO(0.12~16.09wt.%),CaO(0.17~23.41 wt.%)and LOI(8.28-30.06 wt.%).The generally low contents in trace elements(including REE)except for an obvious enrichment in Pb,and the positive Ce anomalies(δCePAAS=1.04~1.95)and negative Pr anomalies(δPrPAAS=0.67~0.93),as well as the variable ratios ofδEuPAAS(0.72~1.71),La/YbPAAS(0.26~1.60)and Y/Ho(26~57)suggest that the precursors to the sulfide-carbonate facies BIF mainly are metalliferious sediments from deep-marine hydrotheral source with minor detrital components.The T2DM ages(ca.2.0 Ga)imply that the Shilu BIFs and interbedded host rocks contain a component with Paleoproterozoic crustal residence age due to a significant crustal accretion event at ca.2.0 Ga in Hainan Island.In connection with the petrographical and mineralogical relationship,we conclude that the precursor precipitates to the Shilu BIFs are variable degree of admixtures of the Fe-Co-Cu-(Si)-rich hydrothermal fluids and detrital components from seawater and fresh water carring continental landmass;whereas the protolith to the main interbedded host rocks,i.e.the pyroxene-amphibole rocks,most likely was terrigenous,fine-grained clastic-sediments but with significant input of hydrothermal fluids in a seawater environment.As a result,a continent marginal marine basin is proposed for deposition of the Shilu BIFs and interbedded host rocks.Sea-level fluctuations caused by marine transgression–regressions possibly contributed to changes in the composition and varied input of the terrigenous sediments.展开更多
基金Supported by Project of China Geological Survey(No.12120113098300)
文摘Quartz porphyry in Yuejinshan Fe-polymetallic deposit is one of the rock masses, which formed the granite belt relating to the late Yanshanian skarn-type Fe-polymetallic deposits in the eastern Heilongjiang, and is also closely related to the metallogenic space of the Fe-polymetallic deposits. Quartz porphyry has the zircon U-Pb concordia age of 125.0±1.1 Ma, overall showing high Si(SiO_2=74.48%--75.00%), rich alkaline(Na_2O+K_2O=7.93%--8.17%, K_2O/Na_2O=1.39--1.46), and poor Mg(MgO=0.27%--0.31%), with the A/CNK value being 0.95--0.99, having the characteristics of obvious enrichment of LREE and medium Eu negative anomaly(0.69--0.74), indicating that the rock belongs to quasi-aluminous high potassium calc-alkaline series and has the same characteristics as those of the I-type granite. The rock is also characterized by the enrichment of LILE and active incompatible elements, and depletion of HFSE such as Nb, Ta, P and Ti, with the Mg~# value being 32--37, indicating that the rock originated from partial melting of crustal materials. It can be concluded from the above characteristics or data and from the distribution of contemporary magmatic rocks in the area, that quartz porphyry in Yuejinshan Fe-polymetallic deposit was formed in a tectonic background of the subduction of the paleo-Pacific plate in late Yanshanian.
文摘The Shilu Fe-polymetallic ore deposit,a famous hematite-rich Fe-ore deposit,is situated at the western Hainan Province of south China.The deposit characterizes the upper Fe ores and the lower Co-Cu ores,which are mainly hosted within a low-grade to medium-grade,dominantly submarine metamorphosed siliciclastic and carbonate sedimentary succession of the Neoproterozoic Shilu Group.Three facies types of metamorphosed BIFs,i.e.the oxide facies,the silicate-oxide facies and the sulfide-carbonate facies BIFs,are identified within the sixth sequence of the Shilu Group.The oxide facies BIF(i.e.the Fe-rich itabirites or ores)consists of alternating hematite-rich microbands with quartz-rich microbands;the silicate-oxide facies BIF(i.e.the Fe-poor itabirites or ores)comprises alternating millimeter-to a few tens meter-scale,magnetite-hematite-rich bands with calcsilicate-rich(garnet+actinolite+diopside+epidote+quartz)meso-to microbands;and the sulfide-carbonate facies BIF(i.e.the Co-Cu ores)contains alternating macro-to mesobands of Co-bearing pyrite and pyrrhotite,and chalcopyrite with mesobands of dolomite+calcite+diopside+quartz and/or chlorite+sericite+quartz.The blastooolitic,blastopelletoid blastocolloidal and blastopsammitic textures,and blasobedding structures which most likely represent primary sedimentation are often observed in these BIF facies.The interbedded host rocks with the BIFs mainly are the pyroxene-amphibole rocks and the banded or impure dolostones,and also contain banded or laminated structures,and lepido-gra-noblastic,nematoblastic and/or blastoclastic textures.Compositionally,the main host rocks,the pyroxene-amphibole rocks contain basic-intermediate SiO_2(~54.00 wt.%),CaO(~14.19 wt.%),MgO(~9.68 wt.%)and Al_2O_3(~8.49 wt.%)with a positive correlation between Al_2O_3 and TiO_2.The UCC-like Zr and Hf abundances,high Ba content andεNd(t)value(^-5.99)as well as the ratios of La/YbPAAS(0.17~1.00),δEuPAAS(0.88~1.12)andδCePAAS(0.93~1.13)commonly reveal that the protoliths to this type rocks are hydrogenic with a large contribution of terrigenous sediments and minor hydrothermal input.The high CaO+MgO+LOI contents and the extremely low trace element and REEconcentrations as well as the ratios of Y/Ho(44~45),δEuPAAS(1.13~1.57)andδCePAAS(0.69~0.98)reflect a marine origin with minor terrigenous materials for the banded or impure dolostones.Moreover,this type rocks also account for a negativeεNd(t)value(^-7.49).The oxide facies BIF is dominated by Fe_2O_3+FeO(~75.59wt.%)and SiO_2(~20.47 wt.%)with aεNd(t)value of^-6.10.The variable contents in Al_2O_3,TiO 2,K2O,Na2O,Zr,Hf and∑REE,and variable ratios of Y/Ho(24~39)andδEuPAAS(0.86~11.07)suggest the precursor sediments to this facies BIF are admixtures of sea-floor hydrothermal fluids and seawaters with minor involvement of detrital components.Compared to the oxide facies BIF,the silicate-oxide facies BIF is lower in Fe_2O_3+Fe O(~39.81wt.%)and Ba but higher in SiO_2(~42.54 wt.%),Al2O3(~3.60 wt.%),TiO_2(~0.19 wt.%),MgO(~1.12 wt.%),CaO(~9.06 wt.%),K_2O(~0.98 wt.%),Mn and Zr.The ratios of Y/Ho(25~34),La/YbPAAS(0.14-0.74)andδEuPAAS(0.91~1.12)most likely are linked to higher degree of detrital contamintants.While the sulfide-caronate facies BIF is main but variable in Fe_2O_3+Fe O(15.79~57.91 wt.%),SiO 2(0.54~61.52 wt.%),MgO(0.12~16.09wt.%),CaO(0.17~23.41 wt.%)and LOI(8.28-30.06 wt.%).The generally low contents in trace elements(including REE)except for an obvious enrichment in Pb,and the positive Ce anomalies(δCePAAS=1.04~1.95)and negative Pr anomalies(δPrPAAS=0.67~0.93),as well as the variable ratios ofδEuPAAS(0.72~1.71),La/YbPAAS(0.26~1.60)and Y/Ho(26~57)suggest that the precursors to the sulfide-carbonate facies BIF mainly are metalliferious sediments from deep-marine hydrotheral source with minor detrital components.The T2DM ages(ca.2.0 Ga)imply that the Shilu BIFs and interbedded host rocks contain a component with Paleoproterozoic crustal residence age due to a significant crustal accretion event at ca.2.0 Ga in Hainan Island.In connection with the petrographical and mineralogical relationship,we conclude that the precursor precipitates to the Shilu BIFs are variable degree of admixtures of the Fe-Co-Cu-(Si)-rich hydrothermal fluids and detrital components from seawater and fresh water carring continental landmass;whereas the protolith to the main interbedded host rocks,i.e.the pyroxene-amphibole rocks,most likely was terrigenous,fine-grained clastic-sediments but with significant input of hydrothermal fluids in a seawater environment.As a result,a continent marginal marine basin is proposed for deposition of the Shilu BIFs and interbedded host rocks.Sea-level fluctuations caused by marine transgression–regressions possibly contributed to changes in the composition and varied input of the terrigenous sediments.
